Unable to use tablet brush pressure
Is your tablet's pressure sensitivity working in other applications? If not, here's a potential solution to the pressure sensitivity not working:
https://www.drivereasy.com/knowledge/fixed-wacom-pen-pressure-not-working/

It says to go either go to search "Wacom Tablet Preference File Utility" open that application and click "remove all user preferences. Save your preferences then restart your computer.

You can also try updating your Wacom Driver.